Hyperlite Mountain Gear Southwest 40L vs REI Co-op Flash 45
Weight and specs compared for 2026 — and which one to choose.
Ultralight 40L pack in Dyneema Composite Fabric with roll-top closure, hip belt pockets, and a structured back panel for comfort on demanding trails.
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Hyperlite Mountain Gear Southwest 40L vs REI Co-op Flash 45: which should you buy?
If saving weight is your priority, the Hyperlite Mountain Gear Southwest 40L wins — at 796 g it is 394 g (33%) lighter than the REI Co-op Flash 45 (1,190 g). That said, the heavier option may justify the extra grams with more capacity, durability or comfort, so weigh the trade-off against how you'll use it.
See where both rank against everything else in this category on the lightest backpack page, or browse the full gear weight database.